New Batteries..can I..Should I..

[PalmettoSailor]

First heres what I know about my electrical system. The boat has 3 batteries, 2 group 31 for the house bank and a starting battery. Wired to a 1/2/all/off switch. I think the previous owner installed a high amp (90?) alternator and there is a Spa Creek controller that I don't know how to use so just leave off. The shore charger is a Newmar. The bilge pump is wired directly to the house bank. The Group 31's were installed in 2005 and I've found them flat twice over the winter so they have to be replaced.

The boat equipment includes: AB Cold machine, VHF, Small Chart plotter, stereo, autopilot (rarely used while sailing), lights, electric windlass, propane switch. Typical use is long weekends with one or two nights on the hook.

I am not looking for advice to completely rebuild my electrical system for long distance crusing. Just some input on batteries. The simplest path is just replacing the Group 31's. I've been quoted $154.75 for Deka DC31DT 105 AH batteries. Is that a decent deal from what you guys have seen?

Alternately, I was quoted Trojan T-105's at 158.45 or Trojan T-605's at $130 each.

First question is, with the G31's am I correct that the two batteries would provide a total of 105 AH before reacing 50% discharge, the T-105's 225 and the T-605's 210. If so, the T605's are about the same cost as the G31's per amp hour provided.

The second question is can I simply put the 6v batteries in series-paralleled without changing anything else? If so, how much sense would it make? Does anyone have any knowledge of the T-605? Its apparently a lower end model from Trojan but would provide more AH than the two Group 31's at an arguably reasonable price increase.

Would I be better off just replacing the Group 31's and applying the difference in cost towards the purchase of a Honda Eu 2000?

[btrayfors]

At the prices you were quoted, the Group 31s and the golf carts are about the same price per AH.

You're correct that two Group 31's would give you a total of 210AH capacity, or 105AH down to 50%.

However, the two golf carts would not give you double that. Two T-105s each with 225AH @ 6V when connected in series would give you 225AH @ 12V. Or, about 110AH down to 50%....about the same as the two Group 31's.

Re: just replacing the Group 31s or going to golf-carts, there are at least 3 considerations other than price:

1. space -- do you have enough room for the golf-carts?

2. the golf carts connected in series to give 12VDC require one less short cable than do two Group 31's connected in parallel.

3. the golf carts very likely have thicker plates, so may last longer and would be more robust.

You should look into the alternator/regulator setup to be sure you are getting the proper charging from the alternator.

You may be able to do better on these prices. T-105's can be had for as little as $110 (from a golf-cart place in Ohio). Shop around.

Wherever you buy, try to be sure that the batteries are fresh, i.e., don't sit on the shelves very long. New batteries begin to sulfate from the time the electrolyte is added, so you want to get fresh ones.

Bill

[mitiempo]

The golf cart type batteries will be a lot more durable and long lasting than the Deka group 31s. As far as I can tell the T605 is pretty close to a T105 - 58 lbs for the T605 vs 62 lbs for the T105. But there is another alternative. Exide GC2 6 volts which are 220 AH each. They can be had for less than the Trojan and are equally durable based on the people who use them the most - golf courses. There was a thread a while ago with both Maine and Sailingdog recommending the Exide.

I agree you should look into the regulator as without it you won't be taking advantage of the alternator you have.

[PalmettoSailor]

Thanks for the input. I would have to take measurements to fully check, but I'm pretty sure I could fit the GC batteries, though it would entail extra costs for new boxes the wiring to put them in series and a retaining system, but I'm pretty sure it could be done.

Btrayfors, In my previous post I was intending to use 4 GC's so I think I would have 210-225 at 50% if my understanding is correct which seems to jive with your input above.

[mitiempo]

That is correct. 4 golf cart batteries @220 AH each will give you 440 AH @ 12 volts so 220 AH takes them to 50% SOC.

[jarcher]

I seem to recall from my research that golf cart batteries are gel and, as such, require a lower charging voltage than all the other technologies available, like AGM and such. You may want to check on the required charging voltage and if it is lower than what you have you'll have to adjust your alternator and battery charger.

[mitiempo]

Golf cart batteries are available in flooded, gel, and AGM from Trojan and many other manufacturers. The battery that is probably best known, the Trojan T105 is a flooded battery.

[PalmettoSailor]

Originally Posted by mitiempo

The golf cart type batteries will be a lot more durable and long lasting than the Deka group 31s. As far as I can tell the T605 is pretty close to a T105 - 58 lbs for the T605 vs 62 lbs for the T105. But there is another alternative. Exide GC2 6 volts which are 220 AH each. They can be had for less than the Trojan and are equally durable based on the people who use them the most - golf courses. There was a thread a while ago with both Maine and Sailingdog recommending the Exide.

I agree you should look into the regulator as without it you won't be taking advantage of the alternator you have.

I haven't been able to find good prices locally on Exides, but a Golf Cart place near my boat has US battery brand 2200XC's rated at 230 AH for $102 a pop without core credit. Even with the extra gear I'll have to add, this seems like a reasonable alternative to my Group 31 set up, offering double the available juice for maybe $200 total more than just replacing what I have.

Unless someone thinks its a really bad idea, I'm leaning towards trying the US Battery GC's.

It seems like its the best option given the boats equipment and should compromise a modest house bank for our boat as equipped. I'll still have to manage things pretty closely to go more than 2 days without a recharge but I'll sure get further than I would with the G31's. It seems my next project is going to be trying to improve the efficiency of the icebox.

[Freesail99]

You should be able to find Interstate Batteries where you are. They are a fairly well known brand on the east coast.

Specifications

MODEL VOLTS AH 20 HR. RC 25A RC 75A LENGTH WIDTH HEIGHT TERMINALS WEIGHT WET
GC2-RD 6 208 415 107 10.25" 7.12" 11.12" UTL, UT 63 lbs.
GC2-HD 6 216 443 115 10.25" 7.12" 11.12" UTL, UT 64 lbs.
GC2-XHD 6 232 475 122 10.25" 7.12" 11.12" UTL, UT, S 67 lbs.
GC8-HD 8 170 340 128@56A 10.25" 7.12" 11.33" UT, UTL, S, A 68 lbs.

[sailingdog]

I'd also point out that the Johnson Control built batteries that are available at Sam's Club—also golf cart type 6 VDC batteries IIRC—are quite good and about $70 per battery or so.

Of the batteries that Freesail listed, I believe either the GC2-HD or GC2-XHD would work well for you. They're essentially T105 clones.